U.S. Pat. No. 7,922,914, which is incorporated herein by reference in entirety, discloses methods and systems for measuring pressure drop through a filter in the flow path and then using the measured pressure drop, possibly at a normalized state and in conjunction with time and/or other data from the system, to estimate characteristics of the fluid, the filter, and/or a working component supplied with the filtered fluid. Such characteristics could include an operating condition of the filter, the remaining useful life of the filter, the relative contaminant concentration in the fluid, and/or the remaining useful life of a working component supplied with the filtered fluid.
U.S. Patent Application Publication No. US 2011/0307160 A1, which is incorporated herein by reference in entirety, discloses systems, methods, and algorithms for monitoring and indicating filter life. The disclosed systems, methods, and algorithms may be utilized for monitoring and indicating the useful life of a filter in an internal combustion engine.
Filters have a finite service interval, the length of which is governed by the nature and amount of contaminant present in the fluid and conditions of use. Service (or filter change) intervals are normally specified in terms of the distance driven or the length of time before the filter should be replaced or serviced. The common practice of using distance or time to define service intervals is an approximation. In some cases, service intervals may be made based on pressure drop across the filter, but this is not normally done due to cost of adding an additional sensor(s).
Depending on the application, a filter may reach terminal pressure drop earlier or later than the specified service interval. Filters sometimes plug before the specified service interval, particularly when the engine is used in severe duty or dirty environments. This was found through research and experimentation, and is because filter service intervals are established based on expected conditions, not on the conditions that the filter actually experiences.